SMTPUTF8 is one of extended/enhanced SMTP feature. The protocol format was defined in RFC 6531.Latest postfix-3.1, support for SMTPUTF8 feature (since version 2.12) and this is how to install/compile it on CentOS 7.
Install libicu-devel, if it’s not install yet.
# yum -y install libicu-devel
Download postfix-3.1 rpm source
# wget http://repos.oostergo.net/7/SRPMS/postfix-3.1.1-1.el7.centos.src.rpm
Rebuild the source
# rpmbuild --rebuild postfix-3.1.1-1.el7.centos.src.rpm
Upgrade existing postfix
# cd rpmbuild/RPMS/x86_64/ # rpm -Uvh postfix-3.1.1-1.el7.centos.x86_64.rpm postfix-perl-scripts-3.1.1-1.el7.centos.x86_64.rpm
Test it
# telnet localhost 25 Trying ::1... Connected to localhost. Escape character is '^]'. 220 web-server.localdomain ESMTP Postfix ehlo localhost 250-web-server.localdomain 250-PIPELINING 250-SIZE 10240000 250-VRFY 250-ETRN 250-ENHANCEDSTATUSCODES 250-8BITMIME 250-DSN 250 SMTPUTF8